Permeabilities Of Gas Molecules In Highly Fluorinated Polyamide-imides Using Molecular Simulation

Grand Canonical Monte Carlo(GCMC) and Molecular dynamics(MD) simulation were used and COMPASS force field was adopted to discuss the sorption and diffusion properties of the polyamide-imides.First,we focused on the relationship between the chemical structure and the chemical-physical properties of polyamide-imides and the establishment of molecular simulation approach for two polyamide-imides.The only difference between the two systems is the substitution pattern of the phenyl ring in the diamine moiety.The calculated glass transition temperature is in good agreement with the experimental results.The solubility coefficients are within one to two times of the literature results,while diffusion selectivity is close to the reported experimental data.Various properties such as chain conformation,pair correlation function,T_g as well as X-ray and mechanical properties of the polyamide-imides were considered to investigate the microstructure of the polyamide-imides and structure dependence of diffusion properties of gas pair.It has been found that the para-substitution polyamide-imide offered better permeability/permselectivity combinations than its meta-isomer.With the above established molecular simulation analysis for the study of structure-permeability property,we designed five polyamide-imides with different length of oligo(tetrafluoroethene) segments.The sorption and diffusion properties of carbon dioxide have been studied using GCMC and MD methods,respectively.The calculated ratio of diffusion coefficients and solubility coefficients were also consistent with experiment data. With increasing F content in the polyamide-imides,the glass transition temperature of the system decreased and the diffusivity of carbon dioxide increased.